From Derek W. Black posted his article "The Constitutional Limit of Zero Tolerance in Schools" on SSRN. Here is the abstract:

With the introduction of modern zero tolerance policies, schools now punish much more behavior than they ever have before. But not all the behavior is bad. Schools have expelled the student who brings aspirin or fingernail clippers to campus, who does not know that a keychain knife in his backpack, or who reports having taken away a knife from another student in order to keep everyone safe. Despite challenges to these examples, courts have upheld the suspension and expulsion of this good-faith, innocuous behavior. With little explanation, courts have opined that the Constitution places no meaningful limit on the application of zero tolerance policies. Indeed, courts have been so dismissive of constitutional challenges that most scholars all but concede the constitutionality of zero tolerance, arguing instead that schools should voluntarily adopt policy changes. This is incorrect. Although the constitution confers significant discretion on schools to regulate student behavior, that discretion does not include the authority to entirely strip students of their constitutional rights and punish them for any reason a school deems fit. This Article argues that fundamental principles of substantive due process limit zero tolerance. In particular, substantive due process prohibits state actors from (1) treating substantially dissimilarly situated students as though they are the same; (2) disregarding a student’s good-faith mistakes or innocence; and (3) presupposing the answers to due process inquiries so as to render hearings meaningless. Zero tolerance policies breach each of these principles and represent a broad overreach of state power, akin to the sort of state overreaching that the Supreme Court has struck down in related areas of juvenile justice. To comply with due process, the state must consider students’ intent and culpability, along with the potential harm posed by the behavior at issue. Contrary to conventional wisdom, courts can strike down zero tolerance policies that fail to take these steps without re-crafting constitutional doctrine.